Photo-electric tube



July 10, 1934. H. c. RENTSCHLER ET AL 6,

PHOTO ELECTRIC TUBE Filed Feb. 28, 1929 flu: I 0414 a 01100 av F "1. Q1 2 IIQVENTORS HCRENTSCHLER BY DEHEN majw ATTORNEY Patented July 10, 1934 UNITED STATES PATENT OFFICE PHOTO-ELECTRIC TUBE Harvey C. Rentschler, East Orange, and Donald E. Henry, Bloomfield, N. J., assignors to Westinghouse Lamp Company, a corporation of Pennsylvania The invention relates to a photo-electric tube of the type employing as the photo-sensitive material, an oxide or sub-oxide of an alkali metal, such as cesium.

One form of photo-electric tube to which our invention particularly relates comprises an envelope of glass containing a cathode or photosensitive electrode having a surface of silver, with a fllm of an oxide or sub-oxide of an alkali metal, such as caesium thereon. It has been found that when the surface of the cathode is provided with such a film of cesium-oxide or suboxide, that the sensitivity of the tube to light in the red and yellow region of the spectrum is increased several fold. It is essential, however, in order to maintain the sensitivity of the tube in this region, that there be no free caesium or other alkali metal in the envelope.

The method which has been employed, hereittl tofore, in producing photo-electric tubes of this material, is briefly, as follows:

The cathode, which may consist of a plate of silver or silver plated copper, is mounted in the envelope with an anode and after exhaustion of the envelope, oxygen is admitted and a discharge created between the anode and cathode to oxidize the silver. The oxygen is then exhausted and the alkali metal introduced. The bulb and contents are then heated up to efiect a reaction between 2. portion of the caesium and the silver oxide to form a film of cesium-oxide or suboxide, on the cathode. The heating is continued for a sumciently long period and temperature to vaporize the excess free cesium out of the bulb through the exhaust system.

Dimculty has been experienced with this procedure due to the high temperature required to vaporize all the cesium out of the envelope. This must be done with great care and in view of this high temperature baking, it is necessary to employ anall glass manifold on the pumping system.

The process is slow and tedious and not well suited for factory production, wherein it is desirable to employ the regular rubber exhaust connections. This heating may also break down some of the active casium-sub-oxide and result in a tube of low sensitivity.

One of the objects of the present invention is to produce a simplified process of manufacturing a photo-electric tube of this nature.

Another object is to provide a novel means of removing free cesium from a photo-electric tube employing, as the light sensitive material, a compound of caesium.

Other objects and advantages will hereinafter appear.

In accordance with our invention we provide within the envelope a getter substance which is inert or at least less active with respect to the alkali metal than is the oxidized silver surface of the cathode, at the reaction temperature of the silver oxide and alkali metal, but which reacts with the alkali metal at a slightly higher temperature to form solid, stable compounds thereof. The reaction temperature of the getter with the alkali metal should not be so high as to cause the cathode to be heated to the dissociation temperature of the oxide or sub-oxide of the alkali metal when the getter is heated to such reaction temperature.

By the use of such a getter material, the tube, after oxidation of the silver surface of the oathode, may be exhausted, the alkali metal generated, the gas filling, if any, introduced and the tube permanently sealed prior to the production of the film of the sub-oxide of the alkali metal. The film of alkali metal oxide or suboxide may be produced on the cathode by heating the whole tube to a temperature at which the alkali metal reacts with the silver oxide. The excess free alkali metal may then be cleaned-up by heating the getter to the reaction temperature thereof with such metal while the bulb and other contained parts are heated to a suificient temperature to prevent the alkali metal from de-' positing thereon.

The getter preferably consists of a quantity of lead glass constituting a portion of the envelope although a compound may be employed either as a coating on some portion of the bulb or its contents, or in a suitable container or capsule. Other methods of introducing the getter will be apparent, a number of which are disclosed in the accompanying drawing.

Reference is had to the drawing for a more complete understanding of the invention.

Fig. 1 is an elevation of a tube embodying our invention, showing the envelope in section, in which a portion of the glass envelope constitutes the getter material.

Figs. 2, 3, 4 and 5 are fragmentary views of a photo-electric tube showing modified methods of utilizing the getter material.

Referring to Fig. 1, a photo-electric tube is shown comprising an envelope 6 having the upper or body portion 7 formed of lime glass or other glass not attacked by czesium vapor and a lower or neck portion 8 formed of lead glass. The envelope contains a plate cathode 9 which in cross section may be of v-shape or semi-circular and which conveniently may consist of silver or silver plated copper. The cathode 9 is supported from the press 10 by support wires 11 and 12,-the latter of which is joined to a leadingin conductor 13. An anode, in the form of a wire 14, which may be of nickel, is positioned within the concavity of the cathode, and is supported above the press by supports 15 and 16, the former of which is connected to a leading-in wire 1'7.

A capsule 18 is supported above the electrode assembly by a wire 19 welded to the upper end of the anode. The capsule contains a chemical mixture capable, when heated, of generating caesium vapor in the device.

A mixture which we prefer to employ in the capsule 18 consists of czesium-dichromate and silicon, the silicon serving as a reducing agent for the caesium-dichromate. A small proportion of a metal such as misch metal or aluminum may be added to the mixture to expeditethe reaction and "to decrease the reaction temperature.

The method of producing the tube is as follows: After the electrodes are sealed into the envelope, the tube is baked out and exhausted through the exhaust connection 20 in the usual manner. After the bulb has cooled it is filled with oxygen at a pressure of about 1.6 mm. and a direct current discharge is passed between the silver plated copper, as cathode and the wire anode, using about 800 to 1000 volts and a low current of about 60 to 100 milliamperes. This discharge is continued until the proper degree of oxidation has been obtained, which may require only a very short time. The preferred degree of oxidation is obtained when the plate color shows a green color, at least in spots. The oxygen is then pumped out and the capsule 18 heated by high frequency induction current to generate the caesium metal in the tube, and if it is desired to employ a gaseous atmosphere in the tube, argon or other gas is introduced at the proper pressure. The tube is then sealed off.

All of the above operations may be conducted on the usual tube exhaust system using rubber connections to the exhaust manifold. The bulb is next placed in an oven and heated to about 125 C. for about 5 minutes to cause a reaction between the caesium vapor and the oxidized silver. producing probably a sub-oxide of cwsium. At this temperature there is no appreciable reaction between the caesium and the lead glass portion of the envelope so that all the caesium is available for forming the sub-oxide film on the cathode.

The excess cazsium is then cleaned-up by heating the lead glass portion in a second adjacent oven at about 350 to 400 C. at which temperature the caesium reacts with the lead oxide content of the lead glass, forming stable solid cmsium compounds. During this treatment the lime glass portion of the tube is maintained at a temperature of about 125 C. to prevent condensation of the caesium in the lime glass portion of the tube and to drive it over to the lead glass portion. Higher heating of the lime glass portion should be avoided in order not to destroy or impair the caesium oxide or sub-oxide film on the cathode. This heating operation should be continued until the free cesium is entirely cleaned-up but ordinarily 5 to 20 minutes will be sufficient.

The bulb is then thoroughly cooled and a read ing taken to determine the photo sensitivity in the red and yellow portions of the spectrum. II

the emission is below normal, the entire bulb may be again heated for about 3 minutes at 200 to 250 C. generally, the occasional tubes which do not have the normal photo-electric sensitivity after the first treatment will be greatly improved by this latter treatment.

It is absolutely essential to remove all the free caesium from the tube by this clean-up action, since small quantities of free caasium is left in the tube deposit on the cathode and destroy the sensitivity of the tube in the red and yellow region, and tend to cause electrical leakage between the leading-in wires. 4

After the tubes have been heat treated they may be seasoned under normal operating conditions for several hours in order to remove all traces of residual gases in the envelope other than the monatomic gases.

In Fig. 2, we have indicated the getter as consisting of a coating 21 applied to the interior of the neck portion of the bulb. In this case the entire bulb may be constructed of lime glass. A compound which may be used, is lead oxide, applied to the bulb before sealing in the mount.

In Fig. 3, the getter is shown as consisting of a ring of oxidized copper 22 supported on the stem tube 23 and capable of being heated by high frequency induction currents. With this construction the getter may be heated independently of the cathode so that the danger of reducing the caesium sub-oxide film during clean up of the excess caesium, is eliminated. During heating of the getter ring 22 the bulb should be baked to a sufficient temperature to vaporize the free caesium from all parts of the device. In place of using an oxidized copper surface for the getter material, suitable compounds capable of reacting with the caesium may be applied to the ring 22 and heated by induction.

We have shown, in Fig. 4, a getter capsule 24 suspended from one of the electrode supports in a position to be conveniently heated by high frequency induction currents. This capsule may contain a material such as, copper oxide, or spongy lead oxide which when heated above the temperature required to form the cazesium sub-oxide film on the cathode, cleans up the excess caesium.

Fig. 5 shows the getter material in the form of a coil 25 of oxidized copper, having its opposite ends connected to the cathode supports by conductors 26 and 27. A separate leading-in conductor 28 and 29 is provided for each of the cathode supports so that the coil 25 may be heated to the reaction temperature by passing electric current directly therethrough to prevent short circuiting of the coil through the cathode, one of the oathode supports is provided with an insulating bead 26' intermediate the press and the cathode. Any suitable getter material may also be supported within the coil 20 as to be heated thereby.

In employing the various forms of getters illustrated, the casium sub-oxide film is first produced on the cathode and the getter then activated to clean up the excess cesium under such conditions that the caesium sub-oxide film is not decomposed.

It is obvious, that changes may be made in the embodiments described without departing from the invention and we desire to include all such changes within the scope of our invention.

What is claimed is:

l. A photo-electric tube comprising an envelope, an anode and a cathode therein, an alkali metal compound on said cathode, and a getter within said envelope capable of reacting with free alkali metal to form stable solid compounds thereof, said getter being disposed in the neck of the envelope.

2. A photo-electric tube comprising an envelope, an anode and a cathode therein, an alkali metal compound on said cathode, and a getter capable of reacting with tree alkali metal to form stable solid compounds thereof, said getter forming a portion of the envelope.

3. A photo-electric tube comprising an envelope, containing substantially no free alkali metal therein, an anode, a cathode and a getter within the envelope capable of combining with free caesium, and consisting of a metallic oxide, substantially inactive at the formation temperature of the cesium compound on the cathode but active at a higher temperature.

4. A photo-electric tube comprising an envelope, an anode and a cathode therein, a film of caesium sub-oxide on said cathode and a getter within the envelope composed of lead oxide.

5. A photo-electric tube comprising an envelope containing substantially no free alkali metal therein, composed in part of a glass resistant to caesium and in part of lead glass and an electrode in said envelope composed in part of a compound of cesium to form a cathode and an anode within said envelope.

6. A photo-electric tube comprising an envelope, containing substantially no free alkali metal therein, an anode and a cathode therein, a film of cesium sub-oxide on said cathode and a getter within the envelope composed of a metallic oxide capable of combining with free cesium and disposed remote from said cathode.

7. A photo-electric tube comprising an envelope, containing substantially no free alkali metal therein, an anode and a cathode therein, an alkali metal compound on said cathode and a getter within said envelope substantially inactive with said alkali metal at the formation temperature of the alkali metal compound but active with the alkali metal at a higher temperature.

8. A photo-electric tube comprising an envelope, containing substantially no free alkalimetal therein, an anode and a cathode therein, an alkali metal compound on said cathode and a getter constituting a portion of the envelope, said getter being substantially inactive with said alkali metal at the formation temperature of the alkali metal compound but forming a stable compound with the alkali metal at a higher temperature.

9. A photo-electric tube comprising an envelope, an anode and a cathode therein, a film of cesium sub-oxide on said cathode and a getter within the envelope composed of lead oxide and located remote from said cathode so that it may be heated independently of the cathode.

10. A photo-electric tube comprising an envelope, an anode and a cathode therein, the latter electrode having an oxidized silver surface, a film of cmsium sub-oxide on said cathode and a getter within the envelope substantially inactive with cesium at the reaction temperature of cesium and silver oxide but active with caesium at a higher temperature.

11. A photo-electric tube comprising an envelope containing an anode, a cathode of silver having a. film of cmsium sub-oxide thereon and a getter, said getter composed of lead glass.

12. A photo-electric tube comprising an envelope containing an anode, a cathode, a caesium compound on said cathode and a getter in the envelope capable of combining with free caesium at tainer to render said excess alkali metal inefleca temperature below the decomposition temperature of said caesium compound, said getter being disposed in the neck of the envelope.

13. A photo-electric tube comprising an envelope containing substantially no free alkali metal therein, an anode and a cathode therein. a caesium compound on the cathode and a getter within the envelope capable of combining with tree cesium, said getter being disposed within the envelope remote from the cathode so that it may be heated independently of the cathode, and said getter being substantially inactive at the formation temperature of the caesium compound on the cathode, but active at higher temperaures.

14. A photo-electric tube including a container, a plurality of electrodes therein, one of said electrodes having a portion thereof comprising a substance including a photo-sensitive material and means within said container for reacting chemically with excess photo-sensitive material in said container to render said excess material ineffective during the normal operation of said device.

15. A photo-electric tube comprising an envelope, a plurality of electrodes therein, a portion of one of said electrodes being composed of a substance including an alkali metal, a reducible compound also in said envelope for reacting chemically with excess alkali metal in said contive.

16. A photo-electric tube comprising an envelope, a plurality of electrodes therein, one 01' said electrodes having a portion thereof composed of a substance including an alakli metal, and a readily reducible compound of a metal in said envelope for reacting chemically with excess alkali metal in said envelope for converting said alkali metal to a stable and electrically inefiective compound with the products of reaction of said alkali metal and said compound being dimcultly vaporizable.

17. A photo-electric tube comprising an envelope, a plurality oi. electrodes therein, a portion 1 0 of one 01' said electrodes composed of a sub- 3 stancqincluding an alkali metal, and a plate including a metallic oxide for reacting chemically with excess alkali metal in said envelope to render said alkali metal ineifective, said container being substantially free from excess alkali metal.

18. A photo-electric tube comprising an envelope, a plurality of electrodes therein, a portion oi one oi said electrodes being composed of a substance including an alkali metal, and a substance ln said envelope chemically active with the alkali metal to render the same ineffective, but substantially inactive therewith at a temperature below about 125 degrees centigrade.

19. Aphoto-electric tube comprising an envelope, a plurality of electrodes therein, a source of alkali metal therein, said source including a non-hygroscopic alkali metal compound and a reducing agent, and a substance for rendering ineffective excess alkali metal therein after said compound is reduced, said substance adapted to react chemically with said excess alkali metal to render the same stable and electrically ineffective.

20. A photo-electric tube comprising an envelope, a plurality of electrodes therein, one 01' said electrodes including a foundation metal and oxygen, a source oi caesium therein, said source including a non-hygroscopic compound of caesium and a quantity of silicon, and a metal oxide adapt- 150 28. A photo-electric tube comprising an envelope. a plurality of electrodes therein, one of said electrodes having a surface including an oxide of cesium and a substance adapted to react chemig ally with cesium to render said ceseum ineiiec- 24. A photo-electric tube comprising an envelope, an anode and a cathode therein, said cathode having a light sensitive surface comprised in part 0! cesium sub-oxide.

HARVEY C. DONALD E. HENRY. 

